Chemical titration method



Patented Oct. 13, 1942 CHEMICAL TITRATION METHOD and Max Levine, Ames,American Bottlers of Clifford A. Shillinglaw Iowa, assignors toCarbonated Beverages, Washington,

corporation No Drawing. Application May 20, 1940, Serial No. 336,264

6 Claims.

This invention relates to an improvement in the tablet titration methodinvolving the use of barium chloride, potassium-acid-sulphate and theindicator sodium-indigodisulfonate. It is primarily adapted, as anoperating procedure in food processing plants, to the testing forcaustic content of alkaline solutions being used at high temperaturesfor sterilizing bottle and removing foreign matter from them.

The principles upon which the invention is based are the precipitationof the carbonates and phosphates from the alkaline test solution (theseprecipitates remain insoluble and do not interfere with thedetermination described below), combined with the use of an indicatorwhich is not significantly affected by the presenc of milder alkalies,such as silicates and aluminates.

The aluminates which have been found to interfere seriously withprevious titration methods employing other indicators did not interferewith the indicator, sodium-indigodisulfonate, employed herein, becausethe point (pH) at which this indicator changes color is suflicientlyhigh (over pH 12) so that aluminates do not caus any appreciable errorwhen used in the presence of barium chloride and yet, under theseconditions, all of the caustic is determined.

The test is carried out in the following manner:

A definite quantity of the solution to be tested cc.) is placed in asmall glass container and cooled to a temperature below 100 F. To thissolution is now added a tablet of barium chloride for the purpose ofprecipitating the carbonates and phosphates and controlling the effectof other non-caustic alkalies. The indicator employed,sodium-indigodisulfonate, may be added separately as a solution. Ourpreferred method is to use it as an ingredient of the barium chloridetablet in a concentration of approximately 2% by weight of the bariumchloride but if desired it may be incorporated in the acid substancecontaining tablet hereinafter referred to. The mixture is then titratedby adding tablets consisting of solid potassium-acid-sulphate, each ofthese tablets being capable of neutralizing /2% caustic (NaOI-I) in the10 cc. of test solution. By the use of the indicator sodiumindigodisulfonate in the presence of barium chloride only the caustic(sodium hydroxide) alkalinity is shown since such other alkalies asmight not have been precipitated by the barium chloride or which tend togo into solution in the process of titration do not interfere with thedetermination and evaluation of caustic alkalinity. The novelty in usingsodium-indigodisulphonate is further indicated by the fact thatsubstantially accurate results may be secured through its use incombination with the acid potassium bisulfate and without the use ofbarium chloride as a preliminary step.

Tests formerly employed for the determination of caustic alkalinity areinoperative when salts of aluminum are present but the test hereindescribed gives a correct indication of th caustic alkalinity in asolution notwithstanding the presence of aluminum compounds.

After having added the tablet of barium chloride containing theindicator sodium-indigodisulfonate, the solution will be colored green.

One of the acid tablets is then dropped into the solution and pulverizedagainst the bottom of the glass container. When dissolved, if thecaustic strength is less than /2 the color of the solution will becomeblue. If, however, the caustic is more than /2% the color will remaingreen and additional acid tablets must be added. Thesepotassium-acid-sulphate tablets are added one at a time and thoroughlycrushed and mixed with the solution. When a considerable portion of thecausticity has been neutralized by the acid, the color of the mixturechanges-to a greenish grey. This is not the end point. Additionaltablets must be added until the color becomes distinctly blu throughoutth solution. The number of tablets of potassium-acid-sulphate employedto produce the characteristic blue color throughout the solutionmultiplied by /2- gives the per cent caustic in the test solution.Smaller portions than whole tablets, such as half, or even quartertablets, can, of course, be used so that the concentration of causticmay be determined to or /a%. This accuracy is sufficient for all of thepurposes for which this titration method is recommended.

Having described our invention, we claim:

1. A method of titration to determine the caustic strength of solutionscontaining caustic, carbonates, phosphates silicates, and aluminates,singly or in combination, comprising precipitation of the interferingnon-caustic alkalies with barium chloride as barium carbonate, bariumphosphate and barium silicate, rendering visible the caustic conditionof the resultant solution by the indicator sodium-indigodisulfonate andmeasuring the causticity by adding portions of solid potassium bisulfateto said solution, each of the said portions of bisulfate beingequivalent to a predetermined proportion by weight of sodium hydroxide.

2. A method of titration to determine the caustic strength of a solutioncontaining caustic alkali, carbonates, phosphates, silicates, andaluminates comprising precipitation of the interfering alkalies withbarium chloride containing the indicator sodium-indigodisulphonate andmeasuring the causticity of the resultant solution by adding portions ofsolid potassium bisulfate, each of said portions being equivalent to apredetermined proportion by weight of sodium hydroxide.

3. A method of titration to determine caustic strength of a solutionsuch as is commonly used at high temperature for sterilizing bottles andremoving foreign matter, containing caustic alkali, carbonates,phosphates, silicates and aluminates comprising cooling of said solutionto a temperature below 100 F., precipitation of the interferingnon-caustic alkalies with barium chloride, rendering visible the causticcondition of the resultant solution by the indicator sodium-'indigodisulphonate and measuring this causticity by adding portions ofsolid potassium bisulfate each of said portions being equivalent to apredetermined proportion by Weight of sodium hydroxide.

4. A method of titration to determine the caustic strength of a solutionsuch as is commonly used at high temperature for sterilizing bottles andremoving foreign matter, containing caustic alkali, carbonates,phosphates, silicates and aluminates comprising the process of coolingthe solution to a temperature below F., precipitation of interferingnon-caustic alkalies with barium chloride containing the indicatorsodiumindigodisulphonate and determining the causticity of the resultantsolution by adding portions of solid potassium bisulfate, each of saidportions of bisulfate being equivalent to a predetermined proportion byweight of sodium hydroxide.

5. A method of titration to determine the canstic strength of solutionscontaining caustic and aluminates, comprising rendering visible thecaustic condition of said solution by the indicator,sodium-indigodisulphonate, and measuring the causticity by addingportions of solid potassium bisulfate, each of said portions beingequivalent to a predetermined proportion by Weight of sodium hydroxide.

6. A method of titration to determine the caustic strength of solutionscontaining caustic, and aluminates, comprising rendering visible thecaustic condition of said solution by the indicatorsodium-indigodisulphonate, and measuring the causticity by addingportions of solid potassium bisulfate, each of said portions beingequivalent to a predetermined proportion by weight of sodium hydroxide.

CLIFFORD A. SHILLINGLAW. MAX LEVINE.

